Heterotrophic anodic denitrification coupled with cathodic metals recovery from on-site smelting wastewater with a bioelectrochemical system inoculated with mixed Castellaniella species

Although Castellaniella species are crucial for denitrification, there is no report on their capacity to carry out denitrification and anode respiration simultaneously in a bioelectrochemical system (BES). Herein, the ability of a mixed inoculum of electricigenic Castellaniella species to perform simultaneous denitrification and anode respiration coupled with cathodic metals recovery was investigated in a BES. Results showed that 500 mg/L NO₃^--N significantly decreased power generation, whereas 100 and 250 mg/L NO₃^--N had a lesser impact. The single-chamber MFCs (SCMFCs) fed with 100 and 250 mg/L NO₃^--N concentrations achieved a removal efficiency higher than 90% in all cycles. In contrast, the removal efficiency in the SCMFCs declined dramatically at 500 mg/L NO₃^--N, which might be attributable to decreased microbial viability as revealed by SEM and CLSM. EPS protein content and enzymatic activities of the biofilms decreased significantly at this concentration. Cyclic voltammetry results revealed that the 500 mg/L NO₃^--N concentration decreased the redox activities of anodic biofilms, while electrochemical impedance spectroscopy showed that the internal resistance of the SCMFCs at this concentration increased significantly. In addition, BES inoculated with the Castellaniella species was able to simultaneously perform heterotrophic anodic denitrification and cathodic metals recovery from real wastewater. The BES attained Cu²⁺, Hg²⁺, Pb²⁺, and Zn²⁺ removal efficiencies of 99.86 ± 0.10%, 99.98 ± 0.014%, 99.98 ± 0.01%, and 99.17 ± 0.30%, respectively, from the real wastewater. Cu²⁺ was bio-electrochemically reduced to Cu⁰ and Cu₂O, whereas Hg⁰ and HgO constituted the Hg species recovered via bioelectrochemical reduction and chemical deposition, respectively. Furthermore, Pb²⁺ and Zn²⁺ were bio-electrochemically reduced to Pb⁰ and Zn⁰, respectively. Over 89% of NO₃^--N was removed from the BES anolyte during the recovery of the metals. This research reveals promising denitrifying exoelectrogens for enhanced power generation, NO₃^--N removal, and heavy metals recovery in BES.

Effect of nickel (II) on the performance of anodic electroactive biofilms in bioelectrochemical systems

The impact of nickel (Ni²⁺) on the performance of anodic electroactive biofilms (EABs) in the bioelectrochemical system (BES) was investigated in this study. Although it has been reported that Ni²⁺ influences microorganisms in a number of ways, it is unknown how its presence in the anode of a BES affects extracellular electron transfer (EET) of EABs, microbial viability, and the bacterial community. Results revealed that the addition of Ni²⁺ decreased power output from 673.24 ± 12.40 mW/m² at 0 mg/L to 179.26 ± 9.05 mW/m² at 80 mg/L. The metal and chemical oxygen demand removal efficiencies of the microbial fuel cells (MFCs) declined as Ni²⁺ concentration increased, which could be attributed to decreased microbial viability as revealed by SEM and CLSM. FTIR analysis revealed the involvement of various microbial biofilm functional groups, including hydroxyl, amides, methyl, amine, and carboxyl, in the uptake of Ni²⁺. The presence of Ni²⁺ on the anodic biofilms was confirmed by SEM-EDS and XPS analyses. CV demonstrated that the electron transfer performance of the anodic biofilms was negatively correlated with the various Ni²⁺ concentrations. EIS showed that the internal resistance of the MFCs increased with increasing Ni²⁺ concentration, resulting in a decrease in power output. High-throughput sequencing results revealed a decrease in Geobacter and an increase in Desulfovibrio in response to Ni²⁺ concentrations of 10, 20, 40, and 80 mg/L. Furthermore, the various Ni²⁺ concentrations decreased the expression of EET-related genes. The Ni²⁺-fed MFCs had a higher abundance of the nikR gene than the control group, which was important for Ni²⁺ resistance. This work advances our understanding of Ni²⁺ inhibition on EABs, as well as the concurrent removal of organic matter and Ni²⁺ from wastewater.

Recovery of heavy metals from industrial wastewater using bioelectrochemical system inoculated with novel Castellaniella species

Water pollution is a global issue that has drastically increased in recent years due to rapid industrial development. Different technologies have been designed for the removal of pollutants from wastewater. However, most of these techniques are expensive, generate new waste, and focus solely on metal removal instead of metal recovery. In this study, novel facultative exoelectrogenic strains designated Castellaniella sp. A5, Castellaniella sp. B3, and Castellaniella sp. A3 were isolated from a microbial fuel cell (MFC). These isolates were utilized as pure and mixed culture inoculums in a bioelectrochemical system (BES) to produce bioelectricity and treat simulated industrial wastewater. A single-chamber MFC inoculated with the mixed culture attained the highest electricity generation (i.e., 320 mW/m² power density and 3.19 A/m² current density), chemical oxygen demand removal efficiency (91.15 ± 0.05%), and coulombic efficiency (54.81 ± 4.18%). In addition, the BES containing biofilms of the mixed culture achieved the highest Cu, Cr, and Cd removal efficiencies of 99.89 ± 0.07%, 99.59 ± 0.53%, and 99.91 ± 0.04%, respectively. The Cr⁶⁺ and Cu²⁺ in the simulated industrial wastewater were recovered via microbial electrochemical reduction as Cr³⁺ and Cu⁰, respectively. However, Cd²⁺ precipitated as Cd (OH)₂ or CdCO₃ on the surface of the cathodes. These results suggest that a mixed culture inoculum of Castellaniella sp. A5, Castellaniella sp. B3, and Castellaniella sp. A3 has great potential as a biocatalyst in BES for heavy metals recovery from industrial wastewater.

Effects of Functionalization in Different Conditions and Ball Milling on the Dispersion and Thermal and Electrical Conductivity of MWCNTs in Aqueous Solution

In this work, the effects of a functionalization method involving different conditions and milling processes on the dispersion and thermal and electrical conductivity of multiwalled carbon nanotubes were studied. The surfaces of MWCNTs were modified using a mixture of sulfuric and nitric acid as an acid treatment and potassium persulfate and sodium hydroxide as an alkaline treatment to achieve more hydrophilic MWCNTs. The morphological and structural investigations were carried out using transmission electron microscopy and Fourier transform infrared spectroscopy. Furthermore, the dispersion characteristics and thermal and electrical conductivity of the as-prepared water-based nanofluids were measured. As a result, the dispersion characteristics revealed that the best dispersion and stability results were obtained for alkaline-treated MWCNTs using potassium persulfate and sodium hydroxide. The thermophysical study using a thermal conductivity analyzer exhibited that the thermal conductivity of the pristine MWCNT nanofluid (0.1 wt%) was enhanced from 603.5 to 610.4 mW/m·K and the electrical conductivity of the raw MWCNT nanofluid was increased from 16.2 to 125.8 μS/cm at 25 °C after alkaline treatment and milling processes, which were performed using planetary ball milling. Regarding the overall results, the milling process and mild alkaline oxidation process are more environmentally friendly, effective, and convenient for the functionalization of CNTs, without requiring any organic solvents or strong acids.

High Electrochemical Performance Silicon Thin-Film Free-Standing Electrodes Based on Buckypaper for Flexible Lithium-Ion Batteries

Recently, applications for lithium-ion batteries (LIBs) have expanded to include electric vehicles and electric energy storage systems, extending beyond power sources for portable electronic devices. The power sources of these flexible electronic devices require the creation of thin, light, and flexible power supply devices such as flexile electrolytes/insulators, electrode materials, current collectors, and batteries that play an important role in packaging. Demand will require the progress of modern electrode materials with high capacity, rate capability, cycle stability, electrical conductivity, and mechanical flexibility for the time to come. The integration of high electrical conductivity and flexible buckypaper (oxidized Multi-walled carbon nanotubes (MWCNTs) film) and high theoretical capacity silicon materials are effective for obtaining superior high-energy-density and flexible electrode materials. Therefore, this study focuses on improving the high-capacity, capability-cycling stability of the thin-film Si buckypaper free-standing electrodes for lightweight and flexible energy-supply devices. First, buckypaper (oxidized MWCNTs) was prepared by assembling a free stand-alone electrode, and electrical conductivity tests confirmed that the buckypaper has sufficient electrical conductivity (10-4(S m-1) in LIBs) to operate simultaneously with a current collector. Subsequently, silicon was deposited on the buckypaper via magnetron sputtering. Next, the thin-film Si buckypaper freestanding electrodes were heat-treated at 600 °C in a vacuum, which improved their electrochemical performance significantly. Electrochemical results demonstrated that the electrode capacity can be increased by 27/26 and 95/93 μAh in unheated and heated buckypaper current collectors, respectively. The measured discharge/charge capacities of the USi_HBP electrode were 108/106 μAh after 100 cycles, corresponding to a Coulombic efficiency of 98.1%, whereas the HSi_HBP electrode indicated a discharge/charge capacity of 193/192 μAh at the 100th cycle, corresponding to a capacity retention of 99.5%. In particular, the HSi_HBP electrode can decrease the capacity by less than 1.5% compared with the value of the first cycle after 100 cycles, demonstrating excellent electrochemical stability.